(1) Field of the Invention
This invention relates to suitably illuminated display devices, planar or curved, panels or panes such as used in commercial advertising, signage, teachings and decorative purposes, some fine arts forms such as paintings, reliefs, sculpture and jewellery objects. It also relates to ornamental decorative partitions, window panes and stained glass forms where the illuminant can be daylight or an artificial light source. The invention exploits the properties of cholesteric or other chiral liquid crystal coatings deposited on transparent substrates that show intense colours when the reflected light from the image coated panels having a dark backing is viewed and shows complementary colours when the light source is behind the panel and the transmitted light through the panel and image is viewed. It exploits the remarkable property of such liquid crystal coatings where the colours perceived change with the angle of viewing and the angle of illumination. It exploits the fact that the coatings don't absorb light and thus superimposed coatings are transparent to each other and their colours mix additively like coloured lights.
(2) Description of Prior Art
The prior art related to this invention is: (1) Cdn. Pat. No. 956159, issued on Oct. 15, 1974 to E. J. Stevens et al, entitled Polychroic Films; (2) Cdn. Pat. No. 704348, issued on Feb. 23, 1965 to Moray and Doris MacNaughton, entitled Illuminated Decorative Panels; (3) Cdn. Pat. No. 445944, issued on Jan. 6, 1948 to Jean Crotti, entitled Processes for Obtaining Multicoloured Effects Similar to Those of Stained Glass Window and Products Resulting Therefrom; (4) Cdn. Pat. No. 1168905, issued on June 12, 1984 to Aldo Colombo, entitled Extended Temperature Range Thermographic Screen to Detect Temperature Anomalies at the Skin; (5) Cdn. Pat. No. 1110052, issued on Oct. 6, 1981 to James Fergason, entitled Composition for Liquid Crystal Thermometry; (6) Cdn. Pat. No. 1180541, issued on Apr. 2, 1985 to Heino Finkelman et al, entitled Crosslinked Organopolysiloxanes Having Liquid Crystalline Properties; (7) U.S. Pat. No. 3,533,399 filed Aug. 2, 1965 by Newton N. Goldberg et al, entitled Temperature Sensing Means and Methods; and (8) U.S. Pat. No. 3,666,948, filed Jan. 6, 1971 by Bela Mechlowitz et al, entitled Liquid Crystal Thermal Imaging System Having an Undisturbed Image on a Disturbed Background.
In the prior art forms of display panels or panes used in the above mentioned applications, light absorbing pigmented colourants having a limited colour gamut were employed. Liquid crystals of the cholesteric type have a large colour gamut than such colourants and therefore more intense colours can be realized. The colours of prior art display forms or panels are static in the sense that they appear almost the same irrespective of the direction of viewing and illumination. In many cases of advertising, signage, jewellery objects and display applications it is desirable to attract the passer-by's attention. Liquid crystal images fulfill admirably this goal as a drastic colour change is perceived by a viewer as he moves past such a display. This colour change is due to light interference phenomena between the oriented molecular layers of liquid crystal mixtures. In the prior art it has been known that certain light interference dielectric coatings possess also such colour-viewing angle dependence properties. Such coatings, however, have not been used for the display panels referred to as the process and the creation of images is not simple and is expensive. Therefore such interference coatings found applications in large scale mass produced single colour products such as special uniformly coloured panes for windows. In other attempts to achieve viewing angle dependent colour effects vertical coloured strips were mounted on a supporting base (Cdn. Patent No. 956159 ref. 1), resulting in a complicated structure. In the prior art ornamental and stained glass displays have been formed by assembling or fixing together suitably shaped pieces of coloured glass (Cdn. Patent No. 704348 ref. 2 and Cdn. Patent No. 445944 ref. 3). The above mentioned devices or processes are time consuming and the freedom to create complicated and complex images is considerably restricted. These limations, as will be described below, are substantially eliminated by the use of liquid crystal coatings.
This invention deals with the use of cholesteric or other chiral liquid crystal coatings on suitable opaque, transparent, translucent or diffusing planar or nonplanar substrates and may utilize one or more such coated substrates fully or partly overlaying or joined together, side by side or with the surfaces at an angle. In the prior art liquid crystal materials have been applied mostly to flexible substrates such as paper, plastic or rubber membranes. Also the liquid crystal materials, usually cholesterol esters, were encapsulated in small (10-50 .mu.m) plastic capsules or they were imbedded in plastic compounds in order to protect the liquid material from deterioration. In such encapsulated cholesteric liquid crystals however the colours are not as intense, particularly the yellows, oranges and the reds. These products were used mainly for thermography or thermometry (Cdn. Patent No. 1168905 ref. 4; Cdn. Patent No. 1110052 ref. 5; U.S. Pat. No. 3,533,399 ref. 7 and U.S. Pat. No. 3,666,947 ref. 8). They were based on the colour-temperature dependence of some liquid crystal mixtures in which the colour is the indication of the temperature of the object being investigated. To my knowledge the change of colour with angle of viewing of liquid crystals have not been taken advantage of in display forms, panels or panes to date. In the prior art the properties of liquid crystals, of interest to any application, existed within the so called mesomorphic temperature range. Above this range the material becomes a colourless isotropic liquid; below this range it becomes a colourless solid. To date, the mesomorphic temperature range of the liquid crystal mixtures that were chosen for practical products had to coincide with the temperature range such products were intended to operate.